The inhibitory neurotransmitter GABA has a central role in control and tuning of excitatory neuronal activity. GABA can be detected non-invasively using 1H magnetic resonance spectroscopy (MRS). We have recently shown that individuals with more GABA in occipital cortex tend to give smaller responses to visual stimuli as measured by functional magnetic resonance imaging (fMRI), suggesting that individual differences between healthy subjects may be a useful tool to investigate the mechanisms underlying the fMRI response. Understanding the relationship between the metabolic demands of excitatory and inhibitory neuronal activity and the activation recorded by fMRI is an important task in neuroscience. The overall goal of this R21 application is to investigate whether GABA concentration correlates with fMRI activation amplitude across the whole brain. This will be addressed by progressing from task activation fMRI to resting-state fMRI and from multiple single-voxel MRS measurements to spectroscopic imaging (MRSI) of GABA.